1. Field of the Invention
The present invention relates to hot melt adhesives and the like, and in particular to plasticizers and tackifier extenders for hot melt adhesives. More particularly the invention relates to improved hot melt adhesives that incorporate enhanced polyisobutylene (PIB) modifiers therein. The invention also relates to methods for improving the peel strength and tack strength of hot melt adhesives by incorporating therein an enhanced PIB modifier.
2. The Prior Art Background
Hot melt adhesives are well known products having many uses, including, for example, and without limitation, use in connection with packaging, woodworking, and bookbinding. Generally speaking, hot melt adhesives are thermoplastic polymer based adhesives. These adhesives are conventionally applied in the molten state, usually at temperatures in the range of about 250° F. Hot melt adhesives typically function by mechanical anchorage to bind two or more objects together.
It is known that the adhesive properties of hot melt adhesives may be improved and enhanced by the incorporation therein of modifiers such as plasticizers and tackifier extenders. These modifiers are conventionally incorporated into the adhesive by adding the same to the adhesive formulation during the production of the adhesive. Generally speaking, tackifier extenders are substances, which may be used in conjunction with conventional tackifiers to achieve the same degree of tack at a lower concentration of the tackifier. Plasticizers are substances that improve the physical characteristics of an adhesive by making it softer and more ductile and perhaps easier to handle and apply.
Conventional hot melt adhesives typically include a base polymer composition, which may be a single polymer or a mixture of polymers, one or more plasticizers, one or more tackifiers, and perhaps other additives such as waxes, fillers, extenders, pigments, and stabilizers such as antioxidants. For example, a styrene-isoprene-styrene block copolymer may be used as a base polymer. Polyterpenes, which are usually solid, may be used as tackifiers. Mineral oils may be used as plasticizers. Conventional polybutenes may be used as combination plasticizers and tackifier extenders. Additives may include fillers such as talc or calcium carbonate, and antioxidants.
As mentioned above, the performance of hot melt adhesives may often be improved and enhanced by the incorporation therein of plasticizers and/or tackifier extenders. A conventional polybutene may often be used as both a plasticizer and a tackifier extender. Such polybutenes are simply added to the hot melt adhesive during formulation. The double bonds of these previously known conventional polybutene materials are mostly internal. That is to say, it is normal for at least about 90% of the double bonds to be at an internal position and for less than about 10% of the double bonds to be in a terminal (vinylidene) position. In addition, while the initial monomeric mixtures used to produce these conventional polybutenes may often be predominantly isobutylene, the same may also incorporates substantial quantities of monomers other than isobutylene. Thus, the conventional polybutenes that have been used as modifiers for hot melt adhesives in the past may generally be referred to as copolymers or terpolymers. For example, such conventional polybutenes often and commonly incorporate approximately 10% or so by weight of 1-butene and/or 2-butene, with only about 90% of the monomeric units in the polymer being isobutylene units.
The incorporation of conventional polybutenes into the hot melt adhesive is accomplished simply by introducing the polybutene into a vessel along with all of the other components of the hot melt adhesive formulation and heating and blending the mixture.